1. Field of the Invention
The present invention relates to semiconductor processing temperature control. More specifically, it relates to controlling the temperature of a semiconductor processing device (target) using a temperature control fluid that is selectively heated and cooled. The temperature of the semiconductor processing device (target) is variable over time according to a predetermined temperature profile.
2. Discussion of the Related Art
Semiconductor device manufacturing involves a large number of processing steps, such as semiconductor crystal growth, wafer cutting, wafer polishing, doping, material depositions, oxide growths, masking, and etching. Because modern semiconductors must be low cost and highly reliable, rapid fabrication with high device yields and with tight tolerances is critical. That generally requires automated equipment and processes in specially designed clean rooms.
While clean rooms are generally successful, they are expensive to build and operate, with the cost being highly dependent on floor space. Thus, only the processing steps that must be performed in a clean room are usually performed there. Furthermore, it is beneficial to minimize the device processing and wafer handling steps required to be performed in a clean room. Many of the steps performed in clean rooms require heating and/or cooling. For example, since etching is highly temperature dependent, the etching temperature of each etching step (there might be several) must be carefully controlled. Increasing etching difficult is that as semiconductors get denser, the need for accurate temperature control becomes greater. Thus, a semiconductor wafer might be etched at a carefully controlled first temperature, then etched at a carefully controlled second temperature, and then etched at a carefully controlled third temperature, and so on.
In prior art semiconductor processing, multiple etchings typically required the semiconductor wafers being processed to be moved between different etching vessels that are maintained at different temperatures. This increased the risk of wafer contamination, necessitated multiple etching vessels and temperature control systems, increased processing time, and increased the required clean room floor space. An alternative was to etch the semiconductor wafers in one vessel at one temperature, remove the semiconductor wafers, change the vessel's temperature, re-insert the semiconductor wafers, and then repeating the process as required. Semiconductor wafer removal was required because it was very difficult or impossible to rapidly change a vessel's temperature, and because it was very difficult or impossible to control the temperature's rate of change.
In clean rooms, temperature control is usually achieved by pumping a temperature control fluid through a semiconductor processing vessel, chamber, tool, device, or assembly, all of which are generically referred to hereinafter as targets. The temperature control fluid is usually heated or cooled using a heat exchanger, with heat flow being dependent on temperature requirements. Typically, electrically controlled valves are used to adjust the control fluid's flow through a heat exchanger. Thus, prior art semiconductor process temperature controls use various types of pipes, pumps, thermostats, heat exchangers, temperature controllers, refrigeration units, heaters, valves, and temperature control fluids.
While beneficial, prior art semiconductor process temperature controls usually either cooled or heated targets, but not both. Systems that both heated and cooled usually used separate temperature control fluids. That is, a fixed volume of temperature control fluid was used for heating, while another fixed volume was used for cooling. Such systems required multiple circulation pipes through the targets, which increased cost and reduced reliability.
However, U.S. Pat. No. 6,026,896 discloses a semiconductor process temperature control system in which control valves switch the temperature control fluid that passes through the target (reference FIG. 3, valve 74, and the supporting text of U.S. Pat. No. 6,026,896). U.S. Pat. No. 6,026,896 thus teaches selectively controlling the temperature control fluid (heated or cooled) that flows through the target. While the system disclosed in U.S. Pat. No. 6,026,896 is beneficial, multiple pumps, numerous control valves, and extensive piping are still required. Furthermore, temperature adjustment and regulation requires rapid valve switching and flushing of the temperature control fluid. This can detrimentally impact reliability because of thermal stresses and pressure mismatches between the heating and cooling subsystems. Furthermore, mass mixing between the heated and cooled temperature control fluids leads to increased power consumption because previously heated temperature control fluid must be cooled, while previously cooled temperature control fluid must be heated.
Therefore, a semiconductor temperature process control system that can heat and cool using the same temperature control fluid would be beneficial. Even more beneficial would be a semiconductor temperature process control system that uses only one volume of temperature control fluid and that requires only one temperature control fluid pump. Still more beneficial would be a semiconductor temperature process control system that uses only one volume of temperature control fluid, that uses only one temperature control fluid pump, and that has reduced thermal shock and reduced valve switching. More beneficial yet would be an efficient semiconductor temperature process control system that uses only one volume of temperature control fluid, that uses only one temperature control fluid pump, and that has low thermal shock and reduced valve switching. Such a system having variable temperatures that change according to well-defined temperature profiles (well-controlled rates of temperature change) would be highly beneficial in that such would enable continuous etching of a semiconductor wafer at different temperatures that change according to a predetermined temperature profile.